I think they can help, but one shouldn't get too hung up on them as people can too obsessed. Using them as a guideline is better rather than watching it throughout the day is better. Perhaps using them before you exercise and after is better, and then be flexible with the results.
I have MyFitnessPal on my phone. It is a neat little app but I will admit I have not done much with it. It seems a little tedious. Maybe a little more bother than I need to go to. A lot of times it's just easier to write things down on an index card. Technology can be overkill sometimes!
I did use the Google Fit app for a while. Then I figured that it didn't really help me much. I am doing just as well by simply reminding myself to take a walk every day. It's just a matter of doing it until it becomes a habit. When it becomes a habit, there's no need to use any app to keep on going.
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Few years back, I had a very bad experience of losing weight through weight loss apps, These random apps are not approved by any medical center or institute. So its better to consult a doctor, create a complete weight loss and diet plan of six or eight months and follow it strictly.